Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756100AbaBFK5X (ORCPT ); Thu, 6 Feb 2014 05:57:23 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:61930 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755813AbaBFK5W (ORCPT ); Thu, 6 Feb 2014 05:57:22 -0500 Date: Thu, 6 Feb 2014 10:57:18 +0000 From: Will Deacon To: "Srivatsa S. Bhat" Cc: "paulus@samba.org" , "oleg@redhat.com" , "rusty@rustcorp.com.au" , "peterz@infradead.org" , "tglx@linutronix.de" , "akpm@linux-foundation.org" , "mingo@kernel.org" , "paulmck@linux.vnet.ibm.com" , "tj@kernel.org" , "walken@google.com" , "ego@linux.vnet.ibm.com" , "linux@arm.linux.org.uk" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 08/51] arm, hw-breakpoint: Fix CPU hotplug callback registration Message-ID: <20140206105718.GG26035@mudshark.cambridge.arm.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205220603.19080.80971.stgit@srivatsabhat.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140205220603.19080.80971.stgit@srivatsabhat.in.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Srivatsa, On Wed, Feb 05, 2014 at 10:06:04PM +0000, Srivatsa S. Bhat wrote: > Subsystems that want to register CPU hotplug callbacks, as well as perform > initialization for the CPUs that are already online, often do it as shown > below: > > get_online_cpus(); > > for_each_online_cpu(cpu) > init_cpu(cpu); > > register_cpu_notifier(&foobar_cpu_notifier); > > put_online_cpus(); > > This is wrong, since it is prone to ABBA deadlocks involving the > cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently > with CPU hotplug operations). Hmm, the code in question (for this patch) runs from an arch_initcall. How can you generate CPU hotplug operations at that stage? > Instead, the correct and race-free way of performing the callback > registration is: > > cpu_maps_update_begin(); > > for_each_online_cpu(cpu) > init_cpu(cpu); > > /* Note the use of the double underscored version of the API */ > __register_cpu_notifier(&foobar_cpu_notifier); > > cpu_maps_update_done(); > > > Fix the hw-breakpoint code in arm by using this latter form of callback > registration. I guess you introduce __register_cpu_notifier somewhere earlier in the series, so it's best if you take this all via your tree. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/